1. Field of the Invention
The present invention refers to a satellite communication terminal that controls Tx timing of a ranging signal and a control method thereof, and more particularly, to a method and structure for acquiring frequency hop timing synchronization for an FH-FDMA satellite communication system.
2. Background of the Invention
A frequency hop communication system refers to a system for performing communication while periodically changing a frequency for a Tx/Rx period. To this end, a start time point and an end time point of a frequency hop are needed to be synchronized, which is called frequency hop timing synchronization. The frequency hop timing synchronization is largely classified into coarse timing synchronization and fine timing synchronization. The coarse timing synchronization refers to approximately matching a hop timing error during a Tx/Rx period to ±0.5 hop or less. The fine timing synchronization refers to reducing the hop timing error to a synchronization error allowed by a communication system. Generally, a timing error is reduced to a synchronization error level of less than 5% of hop duration. The present invention relates to a method and structure for acquiring frequency hop timing synchronization for a satellite communication system having very large propagation delay characteristics and includes coarse timing synchronization and fine timing synchronization.
FIG. 1 shows a procedure of acquiring frequency hop timing synchronization by a ground satellite terminal in a satellite communication system. First, the ground satellite terminal acquires Rx frequency hop timing synchronization using a frequency hop pilot signal. After acquiring the Rx synchronization, the ground satellite terminal acquires Tx frequency hop timing synchronization by receiving a frequency hop ranging signal that was transmitted by itself.
The Tx synchronization is determined according to a propagation distance between the satellite repeater and the ground satellite terminal, and the propagation distance may vary depending on a location of the ground satellite terminal in the satellite communication system. Accordingly, when the ground satellite terminal is not aware of a propagation distance to the satellite repeater, a frequency hop signal initially transmitted by the ground satellite terminal is not a synchronized signal. Thus, a collision with a Tx signal of another satellite terminal may occur.